Find the Harmonic Mean $(H.M.)$ of the sequence $\frac{1}{2}, \frac{1}{3}, \frac{1}{4}, \dots, \frac{1}{17}$.

If the $7^{th}$ term of a harmonic progression is $8$ and the $8^{th}$ term is $7$,then its $15^{th}$ term is

If $a, b, c, d$ are in $H.P.$,then

An automobile driver travels from a plane to a hill station $120 \ km$ distant at an average speed of $30 \ km/hr$. He then makes the return trip at an average speed of $25 \ km/hr$. He covers another $120 \ km$ distance on the plane at an average speed of $50 \ km/hr$. His average speed over the entire distance of $360 \ km$ will be:

Let $a, b, c, p, q$ and $r$ be positive real numbers such that $a, b$ and $c$ are in $GP$ and $a^{p} = b^{q} = c^{r}$. Then,

Given $a + d > b + c$ where $a, b, c, d$ are real numbers,then